In this review article,we summarized the study of the weak light nonlinear properties associated with group velocity change in the ruby.The ruby could be reduced to a two-level system,in which population oscillations could lead to a subluminal result.With the modulated TEM00 beam introduced into the ruby,self-phase modulation together with Fraunhofer diffractions and nondegenerate two-wave coupling between different spatial frequency components of the beam occurs at the same time.Population oscillations,self-phase modulation together with Fraunhofer diffractions and nondegenerate two-wave coupling mechanism competes with each other,which brings a new phenomenon of self-superluminal group velocity propagation in the ruby.
A theoretical approach based on differential radiative transport is proposed to quantitatively analyze the selfabsorption and reemission effects on the emission spectrum for right angle excitation–detection photoluminescence measurements,and the wavelength dependence of the reemission effect is taken into account.Simulations and experiments are performed using rhodamine 6G solutions in ethanol as model samples.It is shown that the self-absorption effect is the dominant effect on the detected spectrum by inducing pseudo red-shift and reducing total intensity;whereas the reemission effect partly compensates for signal decrease and also results in an apparent signal gain at the wavelengths without absorption.Both effects decrease with the decrease in the sample concentration and the propagation distance of the emission light inside the sample.We therefore suggest that diluted solutions are required for accurate photoluminescence spectrum measurements and photoluminescence-based measurements.
We experimentally study the wavelength dependence of light propagation in a water suspension of lithium niobate microcrystalline particles.First,the ballistic transmission in the visible range of the suspension is measured.The nonlinear relationship is observed between the transport mean free path and the wavelength of the incident light.Secondly,we measure the coherent backscattering (CBS) of the sample at different wavelengths.The full width at half maximum of the CBS cone at 532 nm is about 1.24 times as large as that at 671 nm.The results indicate that the light with a long wavelength propagates further than the short wavelength light and the localization state of the short one is stronger.Finally,we investigate the light-controllable CBS experiments in the disordered materials of anisotropic scatterers,which show that the configuration of pump light with the longer wavelength and the probe light with the shorter wavelength performs better.
SHI Fan ZHANG XinZheng LI Jun WANG PiDong XU Yan YU XuanYi XU JingJun
In this work, a two-photon polymerization(2PP) processing device was built using the femtosecond laser, and femtosecond laser direct writing was performed on SU-8 photoresist. Due to the 2PP effect of the photoresist caused by the femtosecond laser, the polymeric line with size less than the focal spot size is obtained. Based on the Raman spectroscopy characterization of SU-8 polymer before and after 2PP, we research the dynamic process of femtosecond laser induced 2PP. In Raman spectra, some scattering peaks with large intensity variation, such as 1 108 cm^(-1) and 1 183 cm^(-1), indicate that the asymmetric stretching vibration of C-O-C bond in SU-8 polymer is increased. By comparison, we can find that 2PP only affects the light absorption of initiator, but does not affect the monomer polymerization. It is helpful to understand the interaction of photoresist and femtosecond laser, and plays an important role in quantitatively controlling the polymerization degree of SU-8 polymer and improving the processing resolution of 2PP.
Plasmonic metasurfaces have recently attracted much attention because of their novel characteristics with respect to light polarization and wave front control on deep-subwavelength scales.The development of metasurfaces with reconfigurable optical responses is opening new opportunities in high-capacity communications,real-time holograms and adaptive optics.Such tunable devices have been developed in the mid-infrared spectral range and operated in light intensity modulation schemes.Here we present a novel optically reconfigurable hybrid metasurface that enables polarization tuning at optical frequencies.The functionality of tuning is realized by switching the coupling conditions between the plasmonic modes and the binary isomeric states of an ethyl red switching layer upon light stimulation.We achieved more than 20°nonlinear changes in the transmitted polarization azimuth using just 4 mW of switching light power.Such design schemes and principles could be easily applied to dynamically adjust the functionalities of other metasurfaces.
